1. Field of the Invention
This invention relates generally to transmission lines and more particularly to superconducting transmission lines.
2. Description of the Related Art
Superconductivity is a well-known phenomenon. For example, K. H. Onnes, as early as 1911, demonstrated that the electrical resistance of mercury drops to zero when it is cooled to approximately 4.degree. Kelvin (K).
Superconductivity has many potential uses. For example, superconducting power lines can save a great deal of energy which is otherwise dissipated during transmission. Superconducting magnets, generators, and motors, can be made small and extremely powerful. Superconducting devices known as Josephson junctions are extremely fast electronic switches having very low power consumption. In short, the potential uses for superconducting materials are so many and varied, that a list of possible applications can continue almost ad infinitum.
Despite all of the potential benefits of superconducting devices and structures, they are currently rarely found outside of research laboratories. A major reason for this is that it is extremely difficult and expensive to cool most materials to their superconducting transition temperature T.sub.c. This is because most materials have a transition temperature within a few degrees Kelvin of absolute zero, requiring the use of expensive and hard to maintain liquid helium as a cooling agent. It is the astronomical costs of producing and maintaining liquid helium systems that heretobefore made superconductor applications impractical for most purposes.
On Mar. 2, 1987, M.K. Wu et al., announced superconductivity in multi-phase YBaCuO at temperatures above that of liquid nitrogen in an article entitled "Superconductivity at 93 K in a New Mixed-Phase Y--Ba--Cu--O Compound System at Ambient Pressure", Physical Review Letters, Volume 58, Number 9. This announcement caused considerable excitement in the scientific community because, for the first time, a superconductor material had been discovered which could use liquid nitrogen as a coolant. Since liquid nitrogen cooling systems are at least an order of magnitude less expensive than liquid helium cooling systems, all manner applications for superconductors suddenly became practical after Wu et al.'s discovery.
After Wu et al.'s announcement, superconductor researchers quickly divided into two major groups. One group began to experiment with bulk YBaCuO in order to discover and characterize its properties. The other group began to experiment with thin films of YBaCuO with a focus on integrated circuit technology and the aforementioned Josephson junction device.
Research into other applications for this relatively high-temperature superconductor appear to be lagging. For example, there is no mention in the literature of a practical method for making YBaCuO into a superconductor wire or cable. This is probably due to the fact that multi-phase YBaCuO is a brittle, ceramic type material, which is difficult to form into macrostructures such as wires and cables.
Other brittle materials have, however, been successfully formed into fibers. For example, glass has been drawn into long fibers for optical transmission. An explanation of how optical fibers can be manufactured is found in an article entitled "Drawing Lightguide Fiber", by D.H. Smithgall et al., The Western Electric Engineer, Winter 1980, pp. 49+. However glass is a very different substance than superconducting YBaCuO, and the methods for forming glass into a fiber and for forming YBaCuO into wires differ considerably.